Low-energy short-term cold atmospheric plasma: Controlling the inactivation efficacy of bacterial spores in powders.

The present research work aims to elucidate kinetics and mechanisms of the inactivation of Bacillus subtilis spores by a surface micro-discharge (SMD) - cold atmospheric pressure plasma (CAPP). Regarding industrial applications, the inactivation of spores was also studied for a static layer of a biopolymer powder or film, with an air plasma and at ambient pressure. Close to 4 log10 cycles of inactivation of Bacillus subtilis spores were achieved when exposing spores on flat glass to the SMD-CAPP. This effect can be reached at a very low plasma power density of 5 mW/cm2 in 7 min exposure time. The maximum inactivation level of spores drops when treating corn-starch powder to 2.6 log10 cycles at 7 mW/cm2 plasma power density for 5 min and with a polymer load of 5 mg/cm2. Similar is true for films produced with hydroxymethyl cellulose (HMC). The inactivation efficacy can be tuned and is a function of applied surface energy (product of the plasma power density and the exposure time) and the polymer load. Plasma diagnostics reveal the fundamental importance of reactive nitrogen species (RNS) in the inactivation. Etching of spore hull is supposed to be triggered by the plasma density, while UV-C and UV-B radiation do not contribute directly and significantly to the inactivation effect at least in a biopolymer matrix. Fluidization of a fixed powder layer is supposed to overcome limitations of the inactivation efficacy by reducing the diffusion distance of active plasma species between the source and the sample. The combination of low plasma power density with short treatment time is supposed to reduce the risk of the formation of side-products from the matrix.

Antimicrobial potential of macro and microalgae against pathogenic and spoilage microorganisms in food.

Algae are a valuable and never-failing source of bioactive compounds. The increasing efforts to use ingredients that are as natural as possible in the formulation of innovative products has given rise to the introduction of macro and microalgae in food industry. To date, scarce information has been published about algae ingredients as antimicrobials in food. The antimicrobial potential of algae is highly dependent on: (i) type, brown algae being the most effective against foodborne bacteria; (ii) the solvent used in the extraction of bioactive compounds, ethanolic and methanolic extracts being highly effective against Gram-positive and Gram-negative bacteria; and (iii) the concentration of the extract. The present paper reviews the main antimicrobial potential of algal species and their bioactive compounds in reference and real food matrices. The validation of the algae antimicrobial potential in real food matrices is still a research niche, being meat and bakery products the most studied substrates.

Stevia rebaudiana Bertoni effect on the hemolytic potential of Listeria monocytogenes.

The effect of Stevia rebaudiana Bertoni on the hemolytic potential of Listeria monocytogenes was studied by means of the assessment of the Listeriolysin O (LLO) production. The three factors under study, stevia concentration in the range [0-2.5] % (w/v), incubation temperature (10 and 37°C), and exposure time (0-65h) significantly affected (p≤0.05) the hemolytic activity of L. monocytogenes. Results showed that at the lower incubation temperature the hemolytic potential of the bacterium was significantly reduced, from 100% at 37°C to 8% at 10°C (after 65h of incubation) in unsupplemented substrate (0% stevia). Irrespective of the temperature, 10 or 37°C, supplementation of the medium with stevia at 2.5 % (w/v) reduced the bacterium's hemolytic activity by a maximum of 100%. Furthermore, the time of exposure to 2.5 % (w/v) stevia concentration was also a significant factor reducing the hemolytic capability of L. monocytogenes. The possibility of reducing the pathogenic potential of L. monocytogenes (hemolysis) by exposure to stevia should be confirmed in real food matrices, opening a research niche with a valuable future impact on food safety.

Nonthermal Inactivation of Cronobacter sakazakii in Infant Formula Milk: A Review.

Up-to-date, nonthermal technologies and combinations of them, in accordance with the "hurdle technology" concept, are being applied by different research groups in response to calls by the International Food and Human Health Organizations (ESPGHAN, 2004; FAO/WHO, 2006, 2008) for alternatives to thermal control of Cronobacter sakazakii in reconstituted powdered infant formula milk. This review highlights (i) current knowledge on the application of nonthermal technologies to control C. sakazakii in infant formula milk and (ii) the importance of the application of nonthermal technologies for the control of C. sakazakii as part of the development of strategies in the context of improving food safety and quality of this product.

Synergistic effect of pulsed electric fields and CocoanOX 12% on the inactivation kinetics of Bacillus cereus in a mixed beverage of liquid whole egg and skim milk.

With a view to extending the shelf-life and enhancing the safety of liquid whole egg/skim milk (LWE-SM) mixed beverages, a study was conducted with Bacillus cereus vegetative cells inoculated in skim milk (SM) and LWE-SM beverages, with or without antimicrobial cocoa powder. The beverages were treated with Pulsed Electric Field (PEF) technology and then stored at 5 degrees C for 15 days. The kinetic results were modeled with the Bigelow model, Weibull distribution function, modified Gompertz equation, and Log-logistic models. Maximum inactivation registered a reduction of around 3 log cycles at 40 kV/cm, 360 micros, 20 degrees C in both the SM and LWE-SM beverages. By contrast, in the beverages supplemented with the aforementioned antimicrobial compound, higher inactivation levels were obtained under the same treatment conditions, reaching a 3.30 log(10) cycle reduction. The model affording the best fit for all four beverages was the four-parameter Log-logistic model. After 15 days of storage, the antimicrobial compound lowered Bacillus cereus survival rates in the samples supplemented with CocoanOX 12% by a 4 log cycle reduction, as compared to the untreated samples without CocoanOX 12%. This could indicate that the PEF-antimicrobial combination has a synergistic effect on the bacterial cells under study, increasing their sensitivity to subsequent refrigerated storage.

Pressure inactivation kinetics of Enterobacter sakazakii in infant formula milk.

Survival curves of Enterobacter sakazakii inactivated by high hydrostatic pressure were obtained at four pressure levels (250, 300, 350, and 400 MPa), at temperatures below 30 degrees C, in buffered peptone water (BPW; 0.3%, wt/vol) and infant formula milk (IFM; 16%, wt/vol). A linear model and four nonlinear models (Weibull, log-logistic, modified Gompertz, and Baranyi) were fitted to the data, and the performances of the models were compared. The linear regression model for the survival curves in BPW and IFM at 250 MPa has fitted regression coefficient (R2) values of 0.940 to 0.700, respectively, and root mean square errors (RMSEs) of 0.770 to 0.370. For the other pressure levels, the linear regression function was not appropriate, as there was a strong curvature in the plotted data. The nonlinear regression models with the log-logistic and modified Gompertz equations had R2 values of 0.960 to 0.992 and RMSE values of 0.020 to 0.130 within pressure levels of 250 to 400 MPa, respectively. These results indicate that they are both better models for describing the pressure inactivation kinetics of E. sakazakii in IFM and BPW than the Weibull distribution function, which has an R2 minimum value of 0.832 and an RMSE maximum value of 0.650 at 400 MPa. On the other hand, the parameters for the Weibull distribution function, log-logistic model, and modified Gompertz equation did not have a clear dependence on pressure. The Baranyi model was also analyzed, and it was concluded that this model provided a reasonably good fit and could be used to develop predictions of survival data at pressures other than the experimental pressure levels in the range studied. The results provide accurate predictions of survival curves at different pressure levels and will be beneficial to the food industry in selecting optimum combinations of pressure and time to obtain desired target levels of E. sakazakii inactivation in IFM.